Process for the treatments performed with gasiform corrosive fluids chiefly adapted for textile, paper and the like industries



ilutiol United States Patent C) Julien Dnngler, Basel, Switzerland NoDrawing. Application November 15, 1954 Serial No. 469,032

Claims priority, application Luxemburg November 17, 1953 2 Claims. (Cl.8-1493) The invention relates to aproceSsfor the treatment of cellulosicand like fiber materials executed by means of gaseous corrosive fluidsand it has for its object chiefly to protect simultaneously those partsof the treating machines used, which are made of ferrous or metalssubject to corrosive action by the treating fluids.

As such treatments may be mentioned by way of example the bleaching ofcotton, rayon or like fabrics made of cellulosic fibres. Said treatmentmay be executed advantageously by means of chlorite which may be in thepresent state of technique in the form of a hot solution or of a coldsolution, the product to be treated impregnated with said solution beingthen exposed to the action of an acid in an atmosphereof moist steam.

The bleaching treatment executedin accordance with the above disclosedtechnique provides excellent results as far as the actual bleachingoperation is concerned but it shows serious side effects and drawbacksconsisting in that the fluid evolved during the treatment attacksenergetically all machine parts made of ferrous or made of metal subjectto corrosion, and consequently the machinery employed must bemanufactured from stainless steel containing large proportions ofmolybdenum and provided with a suitable protective coating. Thesecircumstances lead to such expensive machines that the bleachingperformed by means of chlorite has not found any acclaim in practice inspite of excellent results which may be obtained.

The method according to the invention which allows removing the abovementioned drawbacks is characterized by the fact that the product to betreated is impregnated with one or more treating agents in a liquidstate, and at a temperature which is so low that detrimental reactionsare avoided while the actual treatment is preformed by bringing thetreating agent or agents to a raised temperature inside a dry atmosphereso as to form a dry gaseous fluid which may be a vapor or a gas.

According to further feature of my invention, the product to be treatedpreviously impregnated with one or more liquid treating agents is causedto pass through a treating chamber where it is exposed within a dryatmosphere to the application of heat so that the impregnation agent oragents are brought to their boiling temperature, are then evaporated andtransformed into a super-heated vaporized fluid.

According to a further feature of my invention, the

. product to be treated previously impregnated with a treat- Accordingto a still further feature of my invention, the superheated steam enterspreferably the treating chamber in the form of individual jets the speedof which is greater than 5 metres per second, the jets of superheatedsteam having a temperature above 105 C.

According to a further feature of the invention relating moreparticularly to the bleaching of fibres made of cotton, rayon or likecellulosic material, the product to be treated is impregnated with asolution of chlorite and it is then exposed within a heating chamberboth to the action of an activating agent such as formic, hydrochloric,acetic or like acid and to the action of superheated steam flowingrapidly through said chamber.

According to a still further feature of the invention, the product to bebleached is impregnated with a solution of chlorite containing, forexample, 5 grams of chlorite per litre, or even less, the said solutionbeing kept at a temperature of 20 C., after which the product issqueezed inside a foulard so as to lower the amount of impregnatingagent to about of the dry weight of the treated product, the squeezed orpressed product being finally exposed inside a treating chamber to jetsof superheated steam the temperature of which is higher than C. whileformic acid is being sprayed over the product, during said exposure orpreviously thereto, at the rate of about 6 litres of formic acid perhour.

Further features and advantages of the invention will appear uponreading of the following description. As already disclosed, theapplication of certain treatments executed by means of corrosionproducing fluids, is hindered by the corrosive action of the said fluidson ferrous and like metals of the treating machines which are beingused. Among such treatments, the bleaching with chlorite has alreadybeen mentioned. Now, applicant has found that this corrosive action ofthe treating fluids on ferrous and like metals appears only in a hot andmoist atmosphere.

The method according to the invention which is based on said discovery,removes the drawbacks referred to by incorporating the basic treatingagent at a temperature which is so low that all detrimental reactions,such as corrosion of metallic parts, decomposition of treating agents orothers, are avoided, and by executing the actual treatment inside a dryatmosphere through the admission of an amount of heat such that thetreatment agent is brought into the state of a dry gaseous fluid whichmay be a vapor or a gas, i.e. no moisture remaining then inside thetreating chamber. It has been found in practice that under suchconditions, the attack of metals by gaseous treating agents iscompletely avoided.

The heat required for the execution of the above method is preferablyperformed by means of superheated steam devoid of any moisture, thelatent heat of said superheated steam allowing for the incorporation ofa large amount of heat within a unit of time.

During treatment, the impregnated liquid in the product to be treated isevaporated, and the amount of heat applied and the temperature should besuch that the impregnating agent may be brought to its boilingtemperature, is thus evaporated and finally superheated.

In certain treatments of the type referred to, the prodnet to be treatedmay be submitted to the action of various treating agents or compoundsthereof which are to be set in contact with the product to be treatedunder different .condition l'hus, e.g., the product to be" treated maybe 1 irnpregnated"with a liquid treating agent at room tern-" peratureand then exposed, inside a treating chamber filled with a dryatmosphere, simultaneously to the ap plication of heat and to the actionof at least one other treating agent admitted directly inside the saidtreating chamber in any suitable form, the application of heat having avalue such that the treating agents and/or corrosive compounds containedin the latter may be brought into the state of a dry gaseous fluid, suchas vapor or a gas.

When the application of heat is made by means of the admission ofsuperheated steam flowing at a high speed inside a closed circuit, andwhen the treating agent entering directly the treating chamber is in aliquid state, the said agent may be incorporated in the form of finedroplets so as to come into contact with the treated product, in thestate of a superheated vapor.

By way of example, I will disclose hereinafter the application of themethod according to my invention to the bleaching of a cotton fabric bymeans of chlorite.

According to my invention, the fabric weighing e.g. 250 grams per squaremeter, is impregnated with a solution of chlorite containing 10 gramsper litre by passing through a vat containing the said solution andmaintained at room temperature, i.e., about 20 C. However the ratio ofchlorite is not limited to 10 grams per liter. In certain cases goodresults may be obtained with a ratio of 5 grams of chlorite per litreonly, and in the bleaching of artificial fibres the ratio of chloritemay be reduced to 1 gram per litre.

After it has passed through the said vat, the fabric is squeezed in awringing foulard in a manner such that the amount of impregnating liquidmay be reduced to about 90% in weight of the dry fabric, after which thefabric is submitted to the action of formic acid or of like agentproducing the same effect just before it enters the treating chamber.The incorporation of formic acid may be executed either through passageof the fabric inside a bath preferably of a reduced volume, or elsethrough projection of formic acid as a spray of droplets on the surfacesof the product, or again in any other suitable manner. Possibly, theapplication of formic acid may be actually executed inside the treatingchamber.

This being done, the fabric is caused to pass through a treating machinedesigned e.g. after the manner of drying machines and incorporating aheat-insulated chamber containing at either side of the path followed bythe fabric, series of nozzles through which it is possible to drive ontoboth surfaces of the fabric a gaseous fluid conveying the heat.According to the invention, the heat conveying fluid used is constitutedby superheated steam at a temperature preferably above 105 C. andflowing through a closed circuit incorporating reheating means, the flowof superheated steam being preferably above 5 meters per second.

Since such agents used in the bleaching treatment are toxic for humanbeings, the treating machine should be provided with means allowing thefluidtight input and output of the product to be treated and the exhaustof any excess fluid produced inside the machine during the treatment.

The equipment of the treating machine referred to hereinabove is withinreach of conventional technique relating to such treating machines fortextile and like product and requires no further detailed description.

Before the fabric enters the treating chamber, the latter is brought, bymeans of an admission of superheated steam, to a temperaturesufficiently above 100 C. in order to prevent any condensation on thewalls or like structural elements. The steam admitted before the actualtreatment has begun also drives out any air heretofore contained in themachine so that the latter is filled practically only with superheatedsteam (constituting a dry atmosphere) before the treatment begins.

The impregnated fabric containing as disclosed hereinabove 90% of itsown dry weight, a solution of chlorite and furthermore some formic acidenters the treating chamber prepared as described and is submittedtherein to the action of jets of superheated steam projected againstboth its surfaces at a high speed, say, above 5 meters per second. Theformic acid leads to the production of chlorine dioxide (C10 thepresence of which in the fabric produces immediately the desiredbleaching effect.

According to a chief feature of the invention, the actual treatment isthus performed inside a dry atmosphere, 1.e. inside an atmosphereconstituted by superheated steam and the incorporation of heat producedby the superheated steam is furthermore increased to such an extent thatany impregnating liquid still contained in the fed fabric is brought toits boiling point and is evaporated, while any gaseous fluid existing inor formed inside the treating chamber is brought to a dry state, i.e. tothe state of a dry or of dry superheated vapor. Thus any excess solutionof chlorite is brought to the boiling point and evaporated and gaseouschlorine dioxide formed through reaction between the chlorite and theformic acid is brought to superheated condition through said applicationof heat.

It should be remarked that such conditions are quite different fromthose obtained hitherto in any known bleaching treatment according towhich bleaching reaction is performed either inside a hot solution or ina hot and moist atmosphere constituted generally by saturated steam.

In the bleaching treatment disclosed hereinabove, the chlorine dioxideis resorted to although in the prior known methods the same exerts anenergetic corrosive action on ferrous metal parts inside the treatingchamber. As already disclosed hereinabove, applicant has found that thiscorrosive action of chlorine dioxide was caused due to the simultaneouspresence of moisture. Consequently, in the method according to theinvention defined hereinabove, and according to which the operation isexecuted in a dry atmosphere, through the action of dry gaseous fluids,said corrosive action is eliminated and consequently, the novelbleaching method may be executed in a treating machine made of standardferrous or like metals subject to corrosion.

The particular conditions of operation of the method according to myinvention with a view to avoiding corrosive action of the gaseous fluidsresorted to, reduce by no means the efiiciency of the bleachingtreatment itself and allow the attainment of excellent results whichlead to the fact that the fabric thus treated leaves the treatingmachine after a few seconds only and in a state of perfect whiteness. Atthe same time, the water-absorbing properties of the fabric are improvedand any motes remaining or foreign matter still in the fabric after thepreliminary scalding are completely destroyed.

Of course, the modus operandi of the method according to my invention isdisclosed solely by way of a mere exemplification and by no means in alimiting sense and it is possible to modify in any suitable manner theopera tive steps without thereby unduly widening or changing the scopeof the invention. Thus the method is not only applicable to bleachingbut also to any other treatment executed through the use or formation ofmoist corrosive gaseous fluid. The superheated steam forming theheatconveying vehicle to be preferred may be admitted directly as it isinside the treating chamber or else it may be merely formed in thelatter through the superheating of steam admitted in a saturated stateinside said chamber. Furthermore, the superheated steam may be admixedwith further gaseous fluids in any desired proportion according to thetreatment to be executed.

The treating machine to be used may include any arrangement required forthe contemplated treatment.

Various changes and modifications may be made without departing from thespirit and scope of the present invention and it is intended that suchobvious changes and modifications be embraced by the annexed claims.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent, is:

1. The process of bleaching a fibrous product in a treatment machine inwhich ferrous metal parts thereof are. exposed to corrosion by gaseouschlorine dioxide evolved from an impregnating solution of chlorite at aconcentration of at least 1 gram per liter with which the fibrousproduct has been imbued; said process comprising the steps of applyingto the surface of said product an activating agent capable of reactingwith said chlorite solution under the influence of heat and selectedfrom the group consisting of formic acid, hydrochloric acid and aceticacid, impinging separate jets of superheated steam at a temperature ofabove 105 C. and at a rate of speed not less than 5 meters per second onsaid product imbued with said solution and said activating agent duringpassage of said product through said treatment machine, so that saidmachine is filled with a dry superheated atmosphere and said solutionwithin said product is brought to its boiling point, thus etfectuatingevaporation of said solution and transforming the evaporated solutioninto a dry gaseous fluid containing chlorine dioxide gas outside saidproduct for bringing about bleaching action on the product within saidmachine, whereby moisture therein is eliminated thereby tosimultaneously inhibit corrosion of said machine parts.

2. The process of bleaching a fibrous product in a treatment machine inwhich ferrous metal parts thereof are exposed to corrosion by dioxide ofchlorine evolved under the influence of heat from an impregnating liquidin the form of a solution of chlorite, with which the fibrous producthas been imbued; said process comprising the steps of applying to saidproduct an activating agent capable of reacting With said chloritesolution under the influence of heat so as to give ofi dioxide ofchlorine, impinging separate jets of superheated steam at a temperatureof about 105 C. and at a rate of speed not less than 5 meters per secondon said product imbued with said solution and said activating agentduring passage of said product through said treatment machine, andconditioning said jets so that said solution within said product isbrought to its boiling point, thus effectuating at least partialevaporation of said solution and transforming the evaporated solutioninto a dry gaseous fluid containing chlorine dioxide gas outside saidproduct, to complete the bleaching of the product within said machineand to eliminate any moisture therein thereby to simultaneously inhibitcorrosion of said machine parts by said gas.

References Cited in the file of this patent UNITED STATES PATENTS2,357,262 Kaufimann Aug. 29, 1944 2,432,447 Scheiderbauer Dec. 9, 19472,521,340 Carr Sept. 5, 1950 2,670,266 Singler Feb. 23, 1954 2,691,637Waibel Oct. 12, 1954 FOREIGN PATENTS 690,172 Great Britain Apr. 15, 1953OTHER REFERENCES Power, March 1945, p. 71. Wayman et al.: Abst. of appl.Ser. No. 219,135, pub.

June 30, 1953.

1. THE PROCESS OF BLEACHING A FIBROUS PRODUCT IN A TREATMENT MACHINE INWHICH FERROUS METAL PARTS THEREOF ARE EXPOSED TO CORROSION BY GASEOUSCHLORINE DIOXIDE EVOLVED FROM AN IMPREGNATING SOLUTION OF CHLORITE AT ACONCENTRATION OF AT LEAST 1 GRAM PER LITER WITH WHICH THE FIBROUSPRODUCT HAS BEEN IMBUED, SAID PROCESS COMPRISING THE STPS OF APPLYING TOTHE SURFACE OF SAID PRODUCT AN ACTIVATING AGENT CAPABLE OF REACTING WITHSAID CHLORITE SOLUTION UNDER THE INFLUENCE OF HEAT AND SELECTED FROM THEGROUP SONSISTING OF FORMIC ACID, HYDROCHLORIC ACID AND ACETIC ACID,IMPINGING SEPARATE JETS OF SUPERHEATED STEAM AT A TEMPERATURE OF ABOVE105*C. AND AT A RATE OF SPEED NOT LESS THAN 5 METERS PER SECOND ON SAIDPRODUCT IMBUED WITH SAID SOLUTION AND SAID ACTIVATING AGENT DURINGPASSAGE OF SAID PRODUCT THROUGH SAID TREATMENT MACHINE, SO THAT SAIDMACHINE IS FILLED WITH A DRY SUPERHEATED ATMOSPHERE AND SAID SOLUTIONWITHIN SAID PRODUCT IS BROUGHT TO ITS BOILING POINT, THUS EFFECTUATINGEVAPORATION OF SAID SOLUTION AND TRANSFORMING THE EVAPORATED SOLUTIONINTO A DRY GASEOUS FLUID CONTAINING CHLORINE DIOXIDE GAS OUTSIDE SAIDPRODUCT FOR BRINGING ABOUT BLEACHING ACTION ON THE PRODUCT WITHIN SAIDMACHINE, WHEREBY MOISTURE THEREIN IS ELIMINATED THEREBY TOSIMULTANEOUSLY INHIBIT CORROSION OF SAID MACHINE PARTS.